JPS6098136A - Air-fuel ratio control method of internal-combustion engine - Google Patents

Abstract

PURPOSE:To prevent droppage of engine rotation by changing the air/fuel ratio to lean side with predetermined time delay upon transfer from idling to non- idling. CONSTITUTION:Upon rotation of engine by predetermined crank angle from the time point when an idle switch has turned off or when count C=0, it will go to step 142 while if the count is higher than 0 or during the interval from turning off of idle switch untill rotation of engine by predetermined crank angle, it will go to step 140. In step 142, lean correction factor FLEAN corresponding with current suction tube pressure obtained through interpolation or the lean correction factor set in step 140 is applied to operate fuel injecting time TAU. Fuel injection valve is controlled such that fuel of such amount as corresponding with TAU will be injected in next routine.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an air-fuel ratio control method for an internal combustion engine, and in particular,
Related to improvements in lean control in an air-fuel ratio control method that controls the air-fuel ratio to a stoichiometric air-fuel ratio based on an air-fuel ratio feedback correction coefficient obtained from a sensor output, and also controls the air-fuel ratio leaner than the stoichiometric air-fuel ratio under predetermined conditions. .

[Prior art]

Conventionally, a three-way catalyst has been used to simultaneously purify carbon monoxide, hydrocarbons, and nitrogen oxides in exhaust gas.In order to improve the purification rate of this three-way catalyst, 0. Feedback control is performed in which the air-fuel ratio is estimated by detecting the residual oxygen concentration in the exhaust gas using a sensor, and the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio. In performing this feedback control, the 02 sensor outputs and Based on the signal-processed air-fuel ratio signal, the fuel injection time TAU is calculated by multiplying the air-fuel ratio feedback correction coefficient FAF for proportional-integral operation of the fuel injection time.
Therefore, the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by opening the fuel injection valve for a time corresponding to this fuel injection time TAU.

In addition, from the perspective of improving fuel efficiency, under certain conditions during feedback control, that is, at light loads after complete warm-up,
It has been proposed to carry out lean control in which the air-fuel ratio is feedforward controlled to be leaner than the stoichiometric air-fuel ratio.

Feedback control and lean control mentioned above.

Calculate the fuel injection time TAU based on the following m formula. However, TAUG is the learned value when the intake throttle valve is in the idle position, K
G is the learned value when the intake throttle valve is not in the idle position,
F(t) is a correction coefficient such as a warm-up increase coefficient or a start-up increase coefficient, and FLKAN is a 17-ton correction coefficient less than or equal to l. This lean correction coefficient FLIliAN is set to a predetermined value less than 1 (for example, 0.9
8) is adopted, and when the intake throttle valve is opened, a value smaller than the above predetermined value (for example, 0.64) is adopted.

Therefore, according to the fl1 formula above, the lean correction coefficient FL
Feedback control is performed by setting KAN to 1, and the lean correction coefficient FLJ1! By setting AN to a value less than 2, the fuel injection time TAU becomes shorter and lean control is performed. Regarding lean control, when the intake throttle valve is in the idle position, the air-fuel ratio is controlled to the first air-fuel ratio leaner than the stoichiometric air-fuel ratio, and when the intake throttle valve is opened, the air-fuel ratio is controlled to the leaner side than the first air-fuel ratio. The air-fuel ratio is controlled to 2.

Therefore, when the intake throttle valve is opened at the idle position for racing or starting while lean control is being executed, the lean correction coefficient FLKAN decreases immediately after opening, and the air-fuel ratio is controlled to the lean side, causing the engine to rotate. There is a problem that the engine speed drops and the engine speed does not rise smoothly.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an air-fuel ratio control method for an internal combustion engine in which the engine speed does not drop during racing or starting.

[Structure of the invention]

In order to achieve the above object, the present invention provides a first air-fuel ratio on the lean side that is lower than the stoichiometric air-fuel ratio when the intake throttle valve is in the idle position.
In the air-fuel ratio control method for an internal combustion engine, the air-fuel ratio is controlled to a second air-fuel ratio on the lean side than the first air-fuel ratio when the intake throttle valve is opened. It is characterized in that the intermediate fuel ratio is controlled to the first air-fuel ratio for a predetermined period from the time when the engine is opened from the idle position. In order to control the intermediate fuel ratio to the first air-fuel ratio for a predetermined period, the intake throttle valve can be controlled by holding the Node 7 correction coefficient at the idle position' for a predetermined period.

[Embodiments of the invention]

FIG. 1 shows an example of an internal combustion engine pA (engine) equipped with an air-fuel ratio control system to which the present invention is applied.

The air cleaner 2 is connected to a test throttle bay 6 via an inlet pipe 4. One fuel injection valve 8 is installed on the upstream side of the throttle body 6, and on the downstream side of the fuel injection valve 8, there is an intake valve that adjusts the amount of air-fuel mixture sucked into the combustion chamber of the engine in conjunction with the accelerator pedal. A throttle valve 10 is arranged. The intake throttle valve 10 has an idle switch 11 that turns on when the intake throttle valve is at idle position r# (fully closed) and turns 1 when the intake throttle valve is opened, and an idle switch 11 that is based on the intake throttle valve fully closed position. A power switch 12 is installed that turns on when the intake throttle valve opening is equal to or higher than a predetermined value (for example, 3o"c) and turns off when the intake throttle valve opening is less than a predetermined value. , is used for power increase control to compensate for the lack of output during high loads.Furthermore, a pressure sensor I4 is installed downstream of the intake throttle valve 100 to detect the pressure in the intake pipe.

The throttle body 6 is connected to an intake manifold 16 having branch pipes connected to each cylinder of the engine, and the intake manifold 16 includes an intake temperature sensor 18 that measures the intake air temperature from the temperature of the air-fuel mixture passing through the intake manifold. is installed. The upstream bottom portion 165L of the intake manifold 16 is provided with a riser portion 2o through which engine cooling water temperature is circulated to heat the air-fuel mixture.

Reference numeral 22 denotes the engine body of J[(]. A combustion chamber 28 is formed on the bottom surface of the piston 24 and the inner wall of the cylinder 26, and the air-fuel mixture taken in through the intake valve 3o is caused by the spark plug 32. A water jacket 34 is formed around the cylinder 26, and engine cooling water is circulated through the water jacket 34 to cool the cylinder 26 and the like.A water jacket 34 is formed around the cylinder block 36. An engine coolant temperature sensor 38 that detects the temperature of the engine coolant in 34.
is installed.

An exhaust manifold 42 is connected to an exhaust boat (not shown) of the cylinder head 40, and a sensor 44 for detecting the concentration of external oxygen in exhaust gas is attached downstream of the exhaust manifold 42. Furthermore, the exhaust manifold 42 is connected to an exhaust pipe 48 via a catalytic converter 46 filled with a three-way catalyst.

The spark plug 32 is connected via the distributor 5o and the igniter 52 to a control circuit 54 composed of a microcomputer or the like.

The distributor 5o includes an engine rotation angle sensor 56 and a cylinder discrimination sensor 5, each of which includes a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing.
This cylinder discrimination sensor 58 is equipped with 6.
For cylinder engines, the distributor shaft is 1
Every rotation, the engine rotates twice (720℃A
), the engine rotation angle sensor 56 outputs one pulse at a reference position (for example, top dead center of a specific cylinder) every 30° C.A. Note that 51 is a vehicle speed sensor that detects vehicle speed.

The control circuit 54 includes a central processing unit (cpσ) 60 including an arithmetic logic unit and registers, a read-on memory (ROM) 62 that stores control programs, etc., a random access memory (RAM) ft4, and a backup RAM as a nonvolatile memory. (Bu-IRAM) 66, an input/output board (Ilo) ft8, an analog-to-digital converter (ADC) 70, and a bus 72 such as a data bus or a control bus that connects these. A cylinder discrimination signal from the cylinder discrimination sensor 58, an engine rotation speed signal from the engine rotation angle sensor 56, and a power signal from the power switch 'f-12 are input to Ilo a s, and a drive circuit (not shown) is input to Ilo a s. A fuel injection signal for controlling the fuel injection valve 8 and an ignition signal for controlling the igniter 52 are outputted through the fuel injection valve 8 . The ADC 70 also includes an intake pipe pressure signal from the pressure sensor 14, an intake temperature signal from the intake temperature sensor 8, a water temperature signal from the water temperature sensor 38, a vehicle speed signal from the vehicle speed sensor, and an air-fuel ratio signal from the O sensor 44. is input and CPU6
These signals are sequentially converted into digital signals in accordance with instructions from 0. The above-mentioned ROM 62 stores in advance a control program shown in the following processing routine, a lift-off correction coefficient FLL when the intake throttle valve is in the idle position, and a lift-off correction coefficient FLE'AN when the intake throttle valve is open. ing. This lean correction coefficient FLBAN is determined according to the intake pipe pressure as shown in FIG. For engines that determine the basic fuel injection time based on the amount of intake air and engine speed, the lean correction coefficient FLF is adjusted depending on the amount of intake air and large amount of air.
IAN is defined.

The processing routine of this embodiment will be explained below. First, switching between lean control and feedback control will be explained based on the control switching routine shown in FIG. This routine is executed at predetermined intervals, and in step 120, the engine coolant temperature THW is set to a predetermined value (for example, 80
℃) or the rate of change ΔSP of vehicle speed within a predetermined time (for example, 2 gec) in step 121.
Whether the amount of change ΔB P D / 2 sec (hereinafter referred to as second-order differential value) of
By determining whether or not is less than a predetermined value (for example, 30 degrees), it is determined whether the lean control condition is satisfied. Note that whether or not the intake throttle valve opening degree TA is a predetermined value can be determined based on whether or not the power switch is turned on.

- When the engine coolant temperature THW is below a predetermined value, that is, when it is being warmed up, when the second derivative value ΔSPD/2 (8) of the vehicle speed is above a predetermined value, that is, when the engine is accelerating, or when the intake throttle valve opening When TA is above a predetermined value, that is, when the load is high, lean control is impossible, so step +2
At step 5, air-fuel ratio feedback control is performed using the lean correction coefficient FLKANQl, and the process returns. On the other hand, when the judgments in steps 120, 121 and +22 are affirmative, that is, when the load is light after complete warm-up and the vehicle is in a steady running state, lean control is performed at step 126 and the process returns.

Next, a routine for calculating the fuel injection time TAU in the lean control described above will be explained with reference to FIGS. 5 to 7. FIG. 5 shows a routine that is constantly executed. First, in step 128, it is determined whether the idle switch is on or not, thereby determining whether the intake throttle valve is located at the idle position. . When the idle switch is on, the count value C is set to a predetermined value K in step 13o, and when the idle switch is on, the count value C is set to a predetermined value K, and when the idle switch is on, the count value C is set to a predetermined value K.
7'77;)・Figure 6 shows a predetermined crank angle (for example, +
The interrupt routine is executed every 80'' CA), and if the above-mentioned count value C is 0 at step !32 or not 0, the count value C is decremented by 1 at step +34.

In the fuel injection time TAU calculation routine of FIG. 7, it is determined in step 136 whether the idle switch is on, and if the idle switch is on, step 14 is performed.
0, the value of FL_AN is set as the limp correction coefficient FLL when the intake throttle valve is in the idle position, and then the process proceeds to step 142. On the other hand, when it is determined in step +3fi that the idle switch is off, it is determined in step 138 whether the count value C is O. And count value C
When the count value is 0, that is, when the idle switch has changed from on to off, and when the engine has rotated at a predetermined crank angle, the process proceeds to step 142, and when the count value is 0 or more, that is, when the idle switch has changed from on to off. From this point until the engine rotates at a predetermined crank angle, the process proceeds to step +40. At step +42, the lean correction coefficient FL, [! ! AN or step+
The lean correction coefficient set in step 40 is applied to the above equation 111 to calculate the fuel injection time T'AU. Then, in the next routine, the fuel injection valve is controlled so that fuel corresponding to the fuel injection time TAU is injected.

As a result of the above, from the time the idle switch changes from on to off until the engine rotates at the specified crank angle,
The air-fuel ratio is controlled to be the same air-fuel ratio as the air-fuel ratio when the idle switch is turned on.

FIG. 8 shows the control timing of the above embodiment.

As can be understood from the figure, in this embodiment, the phenomenon of the engine rotational speed dropping as indicated by the broken line is prevented.

In the above, an example in which the present invention is applied to an engine equipped with one fuel injection valve has been described, but the present invention can also be applied to an engine equipped with a fuel injection valve for each cylinder in the intake manifold, or an engine equipped with a fuel injection valve for each cylinder in the intake manifold. It can also be applied to an engine in which the basic fuel injection time is determined by Although the above description has been made of air-fuel ratio control that switches between feedback control and single-control, the present invention can also be applied to air-fuel ratio control that performs lean control over the entire range in operating ranges other than high loads. Furthermore, although the predetermined period for maintaining the air-fuel ratio is determined by the crank angle in the above example, the predetermined period may be determined by time.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to prevent a drop in the engine rotational speed during racing or starting during lean control.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of an engine equipped with an air-fuel ratio control system to which the present invention is applied, Fig. 2 is a block diagram showing details of the control circuit shown in Fig. 1, and Fig. 3 is an intake throttle valve. FIG. 4 is a flowchart showing the control switching routine in the embodiment of the present invention; FIG. 5 is a flowchart showing the count value setting routine in the above embodiment; FIG. 6 are interrupts at every predetermined crank angle in the above embodiment 8...Fuel injection valve, 10...Intake throttle valve, 11
...Throttle switch, 54...Control circuit. Agent Tatsuyuki Unuma (and 1 other person) 1F? J Figure 2 Figure 3 One Fumarole %Fi-/+ PMfmrhH9abs) Figure 4 Figure 5 Figure 6 Figure 8 Aitorusui 7,000 OFF

Claims (1)

[Claims] (1) Controlling the air-fuel ratio to a first air-fuel ratio leaner than the stoichiometric air-fuel ratio when the intake throttle valve is in the idle position, and making the air-fuel ratio leaner than the first air-fuel ratio when the intake throttle valve is opened. The method for controlling the air-fuel ratio of an internal combustion engine to a second air-fuel ratio on the side is characterized by controlling the intermediate air-fuel ratio to the first air-fuel ratio for a predetermined period from the time when the intake throttle valve is opened from the idle position. Air-fuel ratio control method for internal combustion engines.